This invention relates to a process for reducing poisonous effects of metal contaminants picked up by a hydrocarbon conversion catalyst during a hydrocarbon conversion process such as the high temperature conversion of a hydrocarbon feedstock containing such metals to a lower boiling product. More particularly, this invention relates to processes for reducing the poisonous effects of metal contaminants without removal of such contaminants from the catalyst, e.g., by a process of passivation.
During a chemical conversion promoted by a catalyst of a hydrocarbon containing metal poisons, the catalyst often becomes more and more deactivated due to the pick up of at least a portion of the metal poisons. Removal of such poisons from the catalyst may restore a substantial amount of the catalytic activity. However, no matter how carefully the process for removing the metal poisons from the catalyst is carried out, some penalty in the form of overall performance is often paid. Accordingly, a simple and straight forward method of overcoming the deleterious effects of the metal poisons or contaminants is desirable.
Catalytically promoted methods for the chemical conversion of hydrocarbons include cracking, hydrocracking, reforming, hydrodenitrogenation, hydrodesulfurization, etc. Such reactions generally are performed at elevated temperatures, for example, about 300.degree. to 1200.degree. F., more often 600.degree. to 1000.degree. F. Feedstocks to these processes comprise normally liquid or solid hydrocarbons which, at the temperature of the conversion reaction, are generally in a fluid, i.e., liquid or vapor, state and the products of the conversion usually are more valuable, lower boiling materials.
Although referred to as "metals", these catalyst contaminants or poisons may be present in the hydrocarbon feed in the form of free metals or relatively non-volatile metal compounds. It is, therefore, to be understood that the term "metal" as used herein refers to either form. Various petroleum stocks have been known to contain at least traces of many metals. For example, Middle Eastern crudes contain relatively high amounts of several metal components, while Venezuelan crudes are noteworthy for their vanadium content and are relatively low in other contaminating metals such as nickel. In addition to metals such as iron naturally present in petroleum feedstocks, petroleum stocks also have a tendency to pick up tramp iron from transportation, storage and processing equipment. Most of these metals, when present in a feedstock, deposit in a relatively non-volatile form on the catalyst during the conversion processes so that regeneration of the catalyst to remove deposited coke does not also remove these contaminants. With the increased importance of gasoline in the world today and the shortages of crude oils and increased prices, it is becoming more and more important to process all portions of a crude source, including those highly metal contaminated crudes, to more valuable products.
The present invention is particularly suitable for passivation poisons in a catalyst utilized in the catalytic cracking of reduced or top crude oil to more valuable products, such as illustrated in U.S. Pat. Nos. 3,092,568 and 3,164,542, the teachings of which are incorporated by reference herein. Similarly, this invention is applicable to processing shale oils, tar sands oils, coal oils and the like where metal contamination of the processing, e.g., cracking, catalyst can occur.